Actually, for archival purposes, sealed games should not be kept in any museum. While I personally collect sealed games, I am also painfully aware that over time, the acidic wrap on many games begins to react with the paper, cardboard, adhesives on labels and ink which also have acids in them. That's why comics, books and paper money are not sealed in regular commercial grade plastic, but rather stored in acid free materials like mylar, etc... If not very carefully climate controlled, all shrinkwrap gets tighter and more brittle or even sticky over time. That's why you'll find other museums including the collection at Stanford removing the wrap on their sealed items. Sealed games just won't last long term, so while you might not have a problem with a game that is 20-30 years old, in 20 years from now when that game is 50 years old and has been exposed to airborne pollutants, heat and cold, UV and other lighting, etc...it will start to degrade.
Grading and sealing are fine for a very small number of collectors with a fairly short term outlook, but for most collectors and for museums, it is a complete waste of money and prevents long-term preservation.